1. Field of the Invention
The present invention relates generally to a double link type suspension system, used for example, in an automotive vehicle, and more particularly to a double wish-bone type suspension system having upper and lower control arms and a shock absorber installed between a vehicle body side and a wheel side.
2. Description of the Prior Art
In connection with automotive vehicles, a variety of double link type suspension systems have been proposed and put into practical use as disclosed, for example, in Japanese Patent Provisional (First) Publication No. 59-96007 (referred hereinafter to as "the first prior art") and in Japanese Patent Provisional (First) Publication No. 60-135314 (referred hereinafter to as "the second prior art"). In a suspension system of the first prior art, an upper section of a knuckle is upwardly extended over a wheel to form an upper end thereof, which upper end is connected through an upper control arm to a vehicle body. In a suspension system of the second prior art, an upper control arm is longer than usual, and a steering axis (kingpin axis) is set irrespective of the upper control arm. Additionally, there exists an automotive structure (not of double link type) (referred to as "the third prior art") in which an end section of a stabilizer bar is attached to a strut whose lower end is secured to a steering knuckle so that torsion is applied to the stabilizer bar along with vertical movement of the wheels.
Now in order to obtain a suitable suspension geometry, the upper control arm of the double link type suspension system is required to ensure a considerable length and therefore cannot be significantly shortened.
The above-summarized prior arts will now be discussed. In the case of the first prior art suspension system, the inboard end of the upper control arm is supported to a vehicle body while the outboard end of the same is connected to the upper end of the knuckle, and additionally the upper control arm cannot be shortened for the above-mentioned reason, thereby allowing a wheel house to extend to the side of an engine compartment in accordance with the length of the upper arm. In addition, a shock absorber is disposed generally parallel with the upwardly extended knuckle upper section. Thus, the width of the wheel house is enlarged, thereby unavoidably, minimizing the width of the engine compartment. Particularly in this first prior art suspension system, since the knuckle disposed parallel with the shock absorber is turned together with the wheel during steering, a sufficient wide space is necessary between them in order to prevent interference therebetween during turning of the vehicle. This wide space necessarily enlarges the width of the wheel house. Furthermore, the turning of the knuckle together with the wheel requires a ball joint large in height dimension for connection between the upper end of the knuckle and the upper control arm, so that the height of the wheel house is unavoidably enlarged.
In the case of the second prior art suspension system, the distance between the upper and lower control arms is relatively small whereby any variation of camber angle and caster angle due to assembly error of suspension system component parts is a relatively high value. Additionally, such camber angle and caster angle greatly change depending upon vertical swing of the upper and lower control arms. These provide an insufficient controllability of vehicle steering.
Furthermore, in the case of the third prior art suspension system which is constructed such that the stabilizer bar end section is attached to the tube of a shock absorber in the strut, the installation section of the stabilizer bar unavoidably swings around with the strut which turns during vehicle steering, so that elasticity of the stabilizer bar causes steering effort or force from variation in accordance with change in steering turn angle of the wheel. In this connection, a relatively large space is required to prevent interference of the swinging-around stabilizer bar with other parts. In order to prevent such swing-around motion of the stabilizer bar end section, a mechanism for absorbing the swing-around motion is necessary between the stabilizer bar end section and the strut, thereby complicating the structure and raising production cost of the suspension system.
Additionally, during turning of the vehicle, an outer side wheel relative to the vehicle turning direction is raised relative to the vehicle body while an inner side wheel is lowered, thereby increasing camber angle and thus reducing the ground contacting area of the wheel. This unavoidably lowers the gripping force of the wheel to the ground, thereby degrading vehicle driving safety.